Diamonds are classified by four main qualities:

Carat (weight), Color, Clarity and Cut.

These are The Four "C"s of Diamond Value.

Originating over 60 years ago, this method of characterizing diamonds allows people to compare one stone to another in an objective way.

Since diamonds are quite valuable, it’s important to have a consistent evaluation method. The four qualities used to determine a stone’s value are often called the 4Cs: one C each for Carat, Clarity, Color and Cut.

CARAT

Diamonds, as well as other gemstones, are measured according to their mass. One carat is equal to 200 milligrams, or 0.2 grams.  Smaller diamonds, those under one carat, are sometimes measured in the point unit. A point is one one-hundredth of a carat, or 2 mg. To understand how much that weighs, a carat is roughly the same as a standard paperclip.

Even a tiny difference in weight can affect a stone’s cost; that is why precision is key. In stones over a carat, weight is stated in decimals, such as 2.06 carats. Smaller diamonds are often measured down to the hundred thousandth of a carat.

The carat weight stems from ancient times when gem traders used the fairly uniform carob seed as a counterweight when weighing gems. The measure was standardized in 1913 in the United States; today, the carat is a standard weight of .2 grams.

COLOR

Traditionally, a completely colorless diamond was considered the ideal gem. Total lack of color in a clear diamond with a beautiful cut – this was the peak of diamond excellence.

Learn more about Diamonds color.

CLARITY

The clarity of a diamond is a measure of how free it is of blemishes and other internal defects called inclusions. Most diamonds have some imperfections, such as tiny crystals or small cracks; diamonds free of these flaws are very rare, and this greatly affects the value of a given stone. All flaws do not influence price in the same way. Some are so small they cannot be seen by an untrained eye, and thus don’t affect the beauty of the diamond. Some inclusions, on the other hand, are noticeable, and their size, quantity, color, location and visibility may affect price.

The Gemological Institute of America (GIA) devised a system to measure a diamond’s clarity using 11 levels; other organizations have similar grading structures, which, like the GIA System, measure the visibility of flaws under ten time magnification by a trained expert. While no diamond is completely perfect, there are some stones that have very minor flaws; these are called flawless, and most jewelry professionals have never even seen one. Using the GIA scale, diamonds are rated from these near-perfect stones, called flawless, to diamonds with obvious inclusions, I3.

The grades are Fl, flawless; IF, internally flawless; VVS1 and VVS2, very, very slightly included, where trained graders find it difficult to see inclusions under magnification; VS1 and VS2, very slightly included, where minor flaws are clearly visible under magnification; SI1 and SI2, slightly included, where a grader can clearly see flaws with magnification; I1, I2, and I3, where inclusions not only can be seen with magnification, but the inclusions may be affecting the brilliance and transparency of the stone.

Most diamonds are said to be in the VS1 to SI range.

CUT

Cut is what gives a diamond its sparkle and brilliance, and the actual cutting of a rough diamond is both an art and a science, as mathematical proportions affect the overall beauty and fire, which is the extent to which light is dispersed throughout the diamond.

Diamond cutters aim to cut a rough, mined diamond to bring out the inner light and sparkle within the stone. However, it takes fantastic skill to cut a diamond precisely.

Following the actual cutting, polishing improves upon the natural beauty of the stone.

Cut and shape, though linked, are not the same thing; the cut refers to how the stone was proportioned and styled, as well as its symmetry and polish. The shape refers to whether it is round, heart-shaped, triangular, etc.

Any shape can have any style cut.

Round brilliant diamonds are the most common and have 57 polished planes known as facets.

A diamond’s cut can greatly impact how large a stone appears.